The invention addresses the sector of lenses for eyeglasses.
More specifically, the invention relates to the technical field of coloured glass lenses.
In effect, in the eyeglasses sector, the need is felt for coloured glass lenses and, in some cases, colour gradient lenses, that is to say, lenses where the colour is distributed non-uniformly over the surface of the lens.
As regards the colouring of plastic wafers, methods which involve dipping the plastic wafer in a dye are known in the prior art, for example from patent document EP1457808.
Examples of applying a method of this kind to plastic lenses are also described in patent documents ITB020070721 and ITB020070722 in the name of the same Applicant as this invention.
These methods are not used for colouring lenses made of glass, however, because a glass lens coloured with a method of this kind would tend to deteriorate rapidly and to lose its colour properties.
Glass lenses are therefore coloured using a different technique, known as physical vapour deposition (PVD), usually accomplished by the application of plasma.
Examples of lenses coloured using the PVD technique are described in patent documents U.S. Pat. No. 6,793,339B1, WO97/22894A1 and US2002/126256A1.
Other examples of multi-layer lenses for eyeglasses are described in patent documents U.S. Pat. No. 8,210,678B1 and US2011/255051A1.
This method, too, however (that is, colouring glass lenses by PVD) has some (at least two) disadvantages.
A first disadvantage is the limited range of colours that can be applied to the lens.
Moreover, the PVD method involves considerable costs, due to the large amount of waste material and to the equipment needed for the process.